Chemical Speciation of the Fe(III)-piroxicam and Fe(III)-tenoxicam Systems in Aqueous Solution

A chemical speciation study of the antiinflamatory drugs piroxicam and tenoxicam was carried out with the Fe(III) ion, under pseudophysiological conditions (T = 37 degrees C and I = 0.15 M). The equilibrium constants for the formation of the Fe(III)-oxicam species were obtained from UV/VIS spectrophotometric data assisted by SQUAD program. The hydrolysis constants of Fe(III) were also refined under the same experimental conditions. For tenoxicam, the constants refined correspond to the species Fe(H(2)tenox)(2)(5+), Fe(Htenox)(2)(3+), Fe(OH)(2)(Htenox)(2)(+), Fe(OH)(2)(tenox)(2)(-), FeH(2)tenox(4+), FeHtenox(3+), Fe(OH)(2)Htenox(+) and Fe(OH)(2)tenox, an analogous model was established to refine the piroxicam constants. The molar absorptivity coefficients for all the species were also calculated.